On the complexity of a hypermap

AbstractIt is shown that the number of g-hypertrees spanning the hyperdual (σ−1, σ−1α) of a hypermap (σ, α) of genus g equals the number of circular permutations ζ such that g(σ, ξ) = g and g(α, ζ) = 0

Magnetic order in lightly doped cuprates: Coherent vs. incoherent hole quasiparticles and non-magnetic impurities

We investigate magnetic properties of lightly doped antiferromagnetic Mott insulators in the presence of non-magnetic impurities. Within the framework of the t-J model we calculate the doping dependence of the antiferromagnetic order parameter using the self-consistent diagrammatic techniques. We show that in the presence of non-magnetic impurities the antiferromagnetic order is more robust against hole doping in comparison with the impurity-free host, implying that magnetic order can re-appear upon Zn doping into lightly hole-doped cuprates. We argue that this is primarily due to the loss of coherence and reduced mobility of the hole quasiparticles caused by impurity scattering. These results are consistent with experimental data on Zn-doped LaSrCuO.Comment: 11 pages, 7 figs, (v2) final version as publishe

Comparative study of macroscopic quantum tunneling in Bi_2Sr_2CaCu_2O_y intrinsic Josephson junctions with different device structures

We investigated macroscopic quantum tunneling (MQT) of Bi$_2$Sr$_2$CaCu$_2$O$_y$ intrinsic Josephson junctions (IJJs) with two device structures. One is a nanometer-thick small mesa structure with only two or three IJJs and the other is a stack of a few hundreds of IJJs on a narrow bridge structure. Experimental results of switching current distribution for the first switching events from zero-voltage state showed a good agreement with the conventional theory for a single Josephson junction, indicating that a crossover temperature from thermal activation to MQT regime for the former device structure was as high as that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high-$T_c$ cuprates, independent of device structures. The switching current distribution for the second switching events from the first resistive state, which were carefully distinguished from the first switchings, was also compared between two device structures. In spite of the difference in the heat transfer environment, the second switching events for both devices were found to show a similar temperature-independent behavior up to a much higher temperature than the crossover temperature for the first switching. We argue that it cannot be explained in terms of the self-heating owing to dissipative currents after the first switching. As possible candidates, the MQT process for the second switching and the effective increase of electronic temperature due to quasiparticle injection are discussed.Comment: 10pages, 7figures, submitted to Phys. Rev.

Il gruppo di Grigorchuk di crescita intermedia

An explicit description of the 2-group of intermediate growth found by Grigorchuk is given. We also give a few preliminary notions concerning finitely generated groups and their growth functions. © 2001 Springer

On the Critical Behavior of the Uniform Susceptibility of a Fermi Liquid Near an Antiferromagnetic Transition with Dynamic Exponent z=2 z = 2

We compute the leading behavior of the uniform magnetic susceptibility, $\chi$, of a Fermi liquid near an antiferromagnetic transition with dynamic exponent $z=2$. Our calculation clarifies the role of triangular ``anomaly'' graphs in the theory and justifies the effective action used in previous work \cite{Hertz}. We find that at the $z=2$ critical point of a two dimensional material, $lim_{q \rightarrow 0} \chi (q,0) = \chi_0 - D T$ with $\chi_0$ and $D$ nonuniversal constants. For reasonable band structures we find that in a weak coupling approximation $D$ is small and positive. Our result suggests that the behavior observed in the quantum critical regime of underdoped high-$T_c$ superconductors are difficult to explain in a $z=2$ theory.Comment: 12 pages, uuencoded Postscript fil

Isolation and Identification of an Antimutagenic Phthalate Derivative Compound from Octopus (Paraoctopus limaculatus)

Purpose: To isolate and evaluate the antimutagenic properties of compounds previously identified in octopus (Paraoctopus limaculatus).Methods: Octopus fractions, previously obtained by a sequential thin layer chromatography (TLC) procedure, were subjected to further fractionation by TLC and their anti-mutagenic activity monitored using Salmonella tester strains TA98 and TA100 with metabolic activation (S9) in Ames test. The isolated fractions were subjected to structural studies by Fourier transformed infrared spectroscopy (FTIR), nuclear magnetic resonance (1H and 13C NMR), and gas chromatography-mass spectrometry.Results: Five new fractions were obtained from a previously isolated and reported anti-mutagenic octopus fraction. Fractions RB21321b2 and RB21321b3 inhibited > 80 % of the mutagenicity induced by 500 ng AFB1 on both tester strains and were selected for chemical/structural characterization. Data from IR and 1H and 13C NMR suggested the presence of phthalate type of compounds. GC-MS analysis revealed 278 m/z for both fractions which is consistent with a butyl isobutyl phthalate structure.Conclusion: Based on the findings, the compound responsible for the high anti-mutagenic activity of the isolated fraction from octopus is 1-butyl-2-isobutyl-phthalate.Keywords: Octopus, Anti-Mutagenic, Paraoctopus limaculatus, 1-Butyl-2-isobutyl-phthalat

Toward a Unified Magnetic Phase Diagram of the Cuprate Superconductors

We propose a unified magnetic phase diagram of cuprate superconductors. A new feature of this phase diagram is a broad intermediate doping region of quantum-critical, $z=1$, behavior, characterized by temperature independent $T_1T/T_{\rm 2G}$ and linear $T_1T$, where the spin waves are not completely absorbed by the electron-hole continuum. The spin gap in the moderately doped materials is related to the suppression of the low-energy spectral weight in the quantum disordered, $z=1$, regime. The crossover to the $z=2$ regime, where T_1T/T_{\rm 2G}^2 \simeq \mbox{const}, occurs only in the fully doped materials.Comment: 14 pages, REVTeX v2.1, PostScript file for 3 figures attached, UIUC-P-93-06-04

Organizational climate assessment using the paraconsistent decision method

The present study aims to show a model of organisational climate assessment through the integration of success codes and the Paraconsistent Decision Method. In this way, contributing to a previous scenario analysis that can return a more precise feedback of the organisational culture conditions of the organisation.(3ortugal